Channel Messaging API

The Channel Messaging API allows two separate scripts running in different browsing contexts attached to the same document (e.g., two IFrames, or the main document and an IFrame, two documents via a SharedWorker, or two workers) to communicate directly, passing messages between one another through two-way channels (or pipes) with a port at each end.

Note: This feature is available in Web Workers

Channel messaging concepts and usage

A message channel is created using the MessageChannel() constructor. Once created, the two ports of the channel can be accessed through the MessageChannel.port1 and MessageChannel.port2 properties (which both return MessagePort objects.) The app that created the channel uses port1, and the app at the other end of the port uses port2 — you send a message to port2, and transfer the port over to the other browsing context using window.postMessage along with two arguments (the message to send, and the object to transfer ownership of, in this case the port itself.)

When these transferable objects are transferred, they are no longer usable on the context they previously belonged to. A port, after it is sent, can no longer be used by the original context.

The other browsing context can listen for the message using MessagePort.onmessage, and grab the contents of the message using the event's data attribute. You could then respond by sending a message back to the original document using MessagePort.postMessage.

When you want to stop sending messages down the channel, you can invoke MessagePort.close to close the ports.

Find out more about how to use this API in Using channel messaging.

Channel messaging interfaces

MessageChannel

Creates a new message channel to send messages across.

MessagePort

Controls the ports on the message channel, allowing sending of messages from one port and listening out for them arriving at the other.

PortCollection

An array of MessagePorts; an experimental solution to allow broadcasting of a message to multiple ports simultaneously.

Examples

Specifications

Browser compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
Channel_Messaging_API
4
12
41
10
10.6
5
≤37
18
41
11
4.2
1.0
close
4
12
41
10
10.6
5
≤37
18
41
11
4.2
1.0
message_event
4
12
Yes
10
10.6
5
≤37
18
No
11.5
4.2
1.0
messageerror_event
60
18
57
No
47
No
60
60
57
47
No
8.0
onmessage
4
12
41
10
10.6
5
≤37
18
41
11
4.2
1.0
onmessageerror
60
18
57
No
47
No
60
60
57
44
No
8.0
postMessage
4
12
41
10
10.6
5
≤37
18
41
11
4.2
1.0
start
4
12
41
10
10.6
5
≤37
18
41
11
4.2
1.0
worker_support
4
12
41
10
≤15
5
≤37
18
41
≤14
5
1.0
Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
Channel_Messaging_API
4
12
41
10
10.6
5
4.4
18
41
11
4.2
1.0
MessageChannel
4
12
41
10
10.6
5
4.4
18
41
11
4.2
1.0
port1
4
12
41
10
10.6
5
4.4
18
41
11
4.2
1.0
port2
4
12
41
10
10.6
5
4.4
18
41
11
4.2
1.0

BCD tables only load in the browser

MessagePort

BCD tables only load in the browser

See also

© 2005–2021 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/API/Channel_Messaging_API